Barclays has fired the starting gun on separating its African business with an $879 million placement, taking its holding down to a notch above 50 percent.

Now it's up to former Barclays boss Bob Diamond to show he has a serious offer for the remaining stake, palatable both to the bank and a wary South African regulator. If he doesn't step up, the disposal is going to be a slog for the British bank, with more bite-sized placements the fall-back option.

Strong Performer

Africa posted a solid return on tangible equity for Barclays in 2015

Source: Company reports

When Barclays said it wanted to rid itself of the African unit in March, it raised the prospect of a placement, a sale or a bit of both. That it's doing a placement two months later (at a discount) suggests there's been no firm offer for all of the stake, or a big enough chunk for Barclays to deconsolidate the holding. It certainly ups the ante in the poker game with Diamond's Atlas Mara, which has been vocal about its interest -- and there's also the hope that it might flush out another buyer.

There were never going to be many takers for this asset, even though it's performed well. What's left of Barclays' Africa stake would still cost about $4 billion -- hardly small change -- and the unit is heavily exposed to South Africa, a country flirting with recession. You'd have to be brave or rich to make a bet like that in this environment. The last big South African bank on the block was Old Mutual's Nedbank in 2010. The sale failed after HSBC walked away and has since turned into a restructuring and potential spin-off.

Submerging Market

South African shares have been hit by emerging-market turmoil and a sinking currency

Source: Bloomberg data

While you might believe Diamond is placed perfectly given the lack of other interest, financing the deal would be a real stretch. Atlas Mara has a market value of $342 million, so funding partners are needed. Sure, Diamond says he's working with investors including Carlyle. But South Africa's regulator would need a lot of persuading to let a private-equity bidder take control of an important bank.

And on the Barclays side, there's no great comfort in the prospect of the asset going to a former CEO under whose watch the bank was fined a record amount for trying to rig Libor. Behind the scenes, the British government will have similar qualms.

Under Pressure

Barclays shares have fallen this year, but less than some rivals

Source: Bloomberg data

So if Bob really is a buyer, he has to submit a concrete offer, designed not just to clear the financial hurdles but the regulatory and political obstacles too. If he does, Barclays will surely hold its nose and do a deal that gives an essential boost to its capital. Failing that, shareholders will need to brace themselves for a long and tortuous journey out of Africa.

This column does not necessarily reflect the opinion of Bloomberg LP and its owners.